GN: refactor third_party/gni

  This fixes the build on Linux (dep on third_party:zlib -> third_party/zlib).

  I've moved declare_args() {} back to each .gn file... seems like args want
  to be as local as possible in GN land.

  Additionally, refactor all the common third_party config and warning flag
  changes into a template, third_party.  This lets it all live together in a
  .gni: at head unwanted_configs can be in a .gni (it's just a variable) but
  config("no_warnings") (and thus third_party_configs) cannot, as configs
  cannot be part of .gni files.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2163653002

Review-Url: https://codereview.chromium.org/2163653002

3 files changed, 25 insertions, 26 deletions

diff --git a/third_party/BUILD.gn b/third_party/BUILD.gn
index 96837d2b3a..1aca3ca9cb 100644
--- a/third_party/BUILD.gn
+++ b/third_party/BUILD.gn
@@ -3,24 +3,19 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("third_party.gni")
-
-# Most third_party code should disable warnings: if we don't maintain the code, warnings are noise.
-config("no_warnings") {
-  cflags = [ "-w" ]
+declare_args() {
 }
-third_party_configs = [ ":no_warnings" ]
+
+import("third_party.gni")
 
 config("libpng_public") {
   include_dirs = [ "libpng" ]
 }
-source_set("libpng") {
+third_party("libpng") {
   public_configs = [ ":libpng_public" ]
-  configs += third_party_configs
-  configs -= unwanted_configs
 
   deps = [
-    ":zlib",
+    "//third_party/zlib",
   ]
   sources = [
     "libpng/png.c",
@@ -44,10 +39,8 @@ source_set("libpng") {
 config("libjpeg-turbo_config") {
   include_dirs = [ "externals/libjpeg-turbo" ]
 }
-source_set("libjpeg-turbo") {
+third_party("libjpeg-turbo") {
   public_configs = [ ":libjpeg-turbo_config" ]
-  configs += third_party_configs
-  configs -= unwanted_configs
 
   sources = [
     "externals/libjpeg-turbo/jcapimin.c",
diff --git a/third_party/third_party.gni b/third_party/third_party.gni
index 813ee385f3..ede698c4af 100644
--- a/third_party/third_party.gni
+++ b/third_party/third_party.gni
@@ -3,13 +3,19 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-declare_args() {
-}
+template("third_party") {
+  source_set(target_name) {
+    forward_variables_from(invoker, "*")
+
+    # Warnings are just noise if we're not maintaining the code.
+    cflags = [ "-w" ]
 
-# Chrome's GN environment sets up a bunch of default configs we don't need/want here.
-unwanted_configs = [
-  "//build/config/clang:extra_warnings",
-  "//build/config/clang:find_bad_constructs",
-  "//build/config/compiler:chromium_code",
-  "//build/config:feature_flags",
-]
+    # Chrome's GN environment sets up a bunch of default configs we don't need/want here.
+    configs -= [
+      "//build/config/clang:extra_warnings",
+      "//build/config/clang:find_bad_constructs",
+      "//build/config/compiler:chromium_code",
+      "//build/config:feature_flags",
+    ]
+  }
+}
diff --git a/third_party/zlib/BUILD.gn b/third_party/zlib/BUILD.gn
index 0fff083a43..6338dba278 100644
--- a/third_party/zlib/BUILD.gn
+++ b/third_party/zlib/BUILD.gn
@@ -3,16 +3,16 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+declare_args() {
+}
+
 import("../third_party.gni")
 
 config("zlib_public") {
   include_dirs = [ "../externals/zlib" ]
 }
-source_set("zlib") {
+third_party("zlib") {
   public_configs = [ ":zlib_public" ]
-  configs -= unwanted_configs
-
-  cflags = [ "-w" ]
 
   sources = [
     "../externals/zlib/adler32.c",